Nitrogen 1

Question 1

Where do the plants/animals we eat get their nitrogen?

Answer 1

from nitrogen fixing bacteria - the diazotrophs

Question 2

What is atmospheric nitrogen fixed to by the nitrogen fixing bacteria?

Answer 2

ammonia

Question 3

What enzyme does the nitrogen fixing bacteria use?

Answer 3

nitrogenase

Question 4

What inhibits the activity of the nitrogenase enzyme?

Answer 4

oxygen

Question 5

What chemical produced by some leguminous plants prevents the inhibition of the nitrogenase enzyme by oxygen?

Answer 5

leghaemoglobin binds to oxygen

Question 6

How is nitrogen fixed to ammonia by nitrogen fixing bacteria then altered to make it available in a form able to be taken up by plants?

Answer 6

through nitrification, ammonium is converted to nitrite and then to nitrate which is a useable form of nitrogen that can be taken up by plants

Question 7

Through what amino acid is nitrogen capable of ‘flowing’ through to other biomolecules?

Answer 7

glutamate

Question 8

Why is glutamate the medium by which other biomolecules receive nitrogen?

Answer 8

it is the only amino acid that is able to obtain its nitrogen directly from NH4 and the only one that is capable of giving up its nitrogen directly

Question 9

What are the names of the 4 amino acids that are found in much higher concentrations in cells than others?

Answer 9

alanine
glutamine
glutamate
aspartate

Question 10

What 2 amino acids are excitatory neurotransmitters?

Answer 10

aspartate and glutamate

Question 11

How do organisms that cannot fix their own nitrogen, preserve the nitrogen that they do have?

Answer 11

by transferring amino groups between different molecules - called transamination

Question 12

What are 3 general principles of transamination?

Answer 12

• no loss or gain of nitrogen
• readily reversible
• one of the 2 substrate pairs is often glutamate

Question 13

Describe the functional group structure of an amino acid.

Answer 13

an amino group (NH3+) attached to a carbon that is also attached to an acid group (COO-)

Question 14

What often reacts with glutamate in transamination?

Answer 14

alpha-ketoacids e.g pyruvate

Question 15

What are the enzymes that are involved in transamination?

Answer 15

aminotransferases

Question 16

What do aminotransferases rely on for their activity?

Answer 16

pyridoxal phosphate cofactor

Question 17

What molecule typically accepts amino groups?

Answer 17

alpha-ketoglutarate (in reverse reaction)

Question 18

What vitamin is pyridoxal phosphate cofactor made from?

Answer 18

vitamin B6

Question 19

What does the pyridoxal phosphate cofactor do during transamination?

Answer 19

transfers the amino group

Question 20

What is the diagnostic value of plasma aminotransferases?

Answer 20

they are intracellular enzymes and so being outside the cell in plasma indicates cell damage

Question 21

What are the 3 circumstances of amino acid oxidative catabolism?

Answer 21

• leftover amino acids from normal protein turn over are broken down
• too many amino acids obtained from diet that we don’t need
• when carbohydrates are in short supply

Question 22

How are dietary proteins metabolised?

Answer 22

they are enzymatically hydrolysed

Question 23

What does pepsin do?

Answer 23

it cuts protein into peptides in the STOMACH

Question 24

What do trypsin and chymotrypsin do?

Answer 24

cut proteins and larger peptides into smaller peptides in the SMALL INTESTINE

Question 25

What do Aminopeptidase and carboxypeptidases A and B do?

Answer 25

degrade peptides into amino acids in SMALL INTESTINE

Question 26

What is the end point of dietary protein degradation?

Answer 26

individual amino acids

Question 27

Why must protein ingested that is surplus to the body’s requirements be catabolised?

Answer 27

there is no storage facility for excess protein